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	<h1 id="firstHeading" class="firstHeading" lang="en">Dynamic range</h1>
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The dynamic range of a scene, photograph or panorama refers to the ratio between the brightest and darkest portions of the image which is accurately captured or observed. A common problem for panorama production is the large range of brightness levels found in many scenes, e.g. from the deepest shadows under a rock, to direct, unfiltered sunlight. A single exposure cannot possibly achieve detail in the shadows, and avoid saturation in the highlights.
</p><p>To understand why dynamic range is such a challenge in panoramic photography, it helps to understand how the human brain eye system copes with the natural range of brightness found in the world.  Typical natural scenes have a dynamic range of about 18
stops (i.e. 18 doublings), and the human eye, at a single pupil dilation, can appreciate about
17 stops (well matched to typical natural, sun-illuminated scenes, not by
accident!). When you allow for the adjustment of human vision to
illumination conditions, the human brain-eye system can appreciate about
30 stops of dynamic range (a factor of 1 billion:1!), from the faintest
star to full-on sunlight. 
</p><p>By contrast, camera and display systems offer far, far less dynamic range.  Good digital cameras may offer only up to 10 stops of dynamic range (i.e. 1,000:1).  Most deliver dynamic range well below that (see <a rel="nofollow" class="external autonumber" href="http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/dynamic_range_01.htm">[1]</a>). Using a camera's <a href="RAW.html" title="RAW">RAW</a> mode gives more control for <a href="Tone_mapping.html" title="Tone mapping">tone mapping</a> the dynamic range captured by the sensors, which may extend the range by 1-1.5 stop at most. See RAW dynamic range extraction<a class="external" href="https://wiki.panotools.org/RAW_dynamic_range_extraction">[*]</a> for details.
</p><p>This is still a factor of ~500 less than is present in typical sun-illuminated scenes, and even that is rarely achieved in practice (see <a rel="nofollow" class="external autonumber" href="http://www.dpreview.com/news/0011/00111701dynamicrange_raw.asp">[2]</a>). Film cameras offer larger dynamic range at the cost of non-linear "roll-off" of shadows and highlights. Some digital cameras apply digital transfer curves to approximate this, and certain cameras (e.g. <a rel="nofollow" class="external autonumber" href="http://www.luminous-landscape.com/reviews/cameras/fuji-s2-pro.shtml">[3]</a>) have special purpose <a href="CCD.html" title="CCD">CCDs</a> to extend dynamic range even further. The problem is even worse when considering display systems.  Typical desktop displays offer about 7-8 stops of contrast (e.g. 100:1), high-end plasma TV's offer
10 stops (1200:1),    
</p><p>This gives you a sense of the problem, and
also poignantly illustrates why it's so hard to get realistic looking moon
shots or other high contrast scenes which are so easy to appreciate using
your eyes, but so hard to capture using photographic techniques.  
</p><p>There are several methods of coping with high dynamic range, including shooting a series of exposures at different exposure times, and combining them digitally afterwards (see Contrast Blending<a class="external" href="https://wiki.panotools.org/Contrast_Blending">[*]</a>) using 16bits per color channel (e.g. Full 16 bit workflow<a class="external" href="https://wiki.panotools.org/Full_16_bit_workflow">[*]</a>) to target the limited range of the output device (printer or display).  There are also several interesting automatic range compression algorithms which have been proposed (e.g. <a rel="nofollow" class="external text" href="http://www.cs.huji.ac.il/~danix/hdr/">Gradient Domain High Dynamic Range Compression</a>).
</p><p>Photoshop CS2 now has an internal merge to HDR function, which can assemble a <a href="Bracketing.html" title="Bracketing">bracketed</a> exposure series into a true HDR image. There is a nice tutorial by Brian Greenstone on how to deal with this: <a rel="nofollow" class="external autonumber" href="http://www.panomundo.com/panos/howto/workflow_expbracketing.html">[4]</a> and a comparison of two plugins that attempt to compress a HDR image here: HDR compression<a class="external" href="https://wiki.panotools.org/HDR_compression">[*]</a>
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